Victims of trauma, burns, sepsis and other serious multi-system illnesses are managed in medical and surgical intensive care units. The incidence of acute renal failures in these settings is very high. Adequate dialysis treatment can be the only hope of survival for these patients.
Such "critical care" patients also need intravenous fluids at high rates, but the infusions must be carefully controlled in accordance with measurements of pressure in the vein to avoid fluid accumulation in the lungs. In addition, various medications, which are often incompatible when mixed together, need to be administered via different intravenous lines. Frequent sampling of blood is also required to assess the progress of the illness as well as the treatments being administered.
Critical care management can be carried out with a single-lumen catheter introduced in a central vein and used intermittently and sequentially for different functions, with some constraints. However, triple-lumen catheters such as those described in U.S. Pat. Nos. 3,995,623 to Blake; 4,406,656 to Hattler et al.; 4,072,146 (Re. 31,873) and 4,894,057 to Howes; 4,795,439 to Guest; and in European Patent Publication EP 0 440 992 A2 by Mahurkar, provide three independent dedicated lumens in a single catheter and opening at different sites in the vein. Such catheters permit simultaneous and continuous monitoring as well as treatment of all parameters, and are devices of choice in managing seriously ill patients. These triple-lumen critical-care catheters, however, are of little use for effective hemodialysis, because their inefficient flow geometry fails to provide a bidirectional blood flow of 250 ml per minute with a pressure gradient under 100 mm of mercury. Most of the time, therefore, a patient using a triple-lumen critical-care catheter also requires the insertion of an additional hemodialysis catheter in his central veins.
Hemodialysis is a process of mass transfer, in which certain chemical substances, accumulated in the blood because of kidney failure, are transferred from the blood across a semipermeable dialysis membrane to a balanced salt solution (dialysate). The quantity of the mass so transferred depends on its concentration in the blood and the volume of blood brought into contact with the dialysis membrane. The efficiency of a hemodialysis catheter, therefore, depends on the amount of a patient's blood that the catheter can deliver to the dialyzer each minute. Normally a hemodialysis catheter should deliver to the dialyzer about 250 millimeters of blood per minute under a pressure gradient of 100 millimeters of mercury, and return the same amount of dialyzed blood back to the patient under the same pressure gradient.
Early methods of dialysis access utilized two surgical cut downs for insertion of catheters, one in an artery and another in a vein. Later, two individual catheters were inserted in a single vein percutaneously (Shaldon's procedure). During the same period, McIntosh et al. described two single-lumen catheters of unequal length joined side by side and placed them in a femoral vein by surgical implantation. Uldall (Canadian patent 1,092,927) and Martin (Canadian patent 1,150,122) described two individual single-lumen catheters, arranged co-axially, one inside the other, for use in a subclavian vein for hemodialysis.
All these methods and devices are now essentially obsolete because of the need for two surgical insertion procedures for the single-lumen catheters, and the inefficient flow geometry of the co-axial catheters.
Efficient catheters incorporating semicircular flow geometry in parallel flow paths to provide high bidirectional blood flow rates, with axial separation of lumen ends to avoid admixture, are described in U.S. Pat. Nos. 4,134,402, Des. 272,651, 4,568,329, 4,692,141, 4,583,968, 4,770,652, 4,808,155, 4,842,582 and 4,895,561, and Canadian patent 1,193,508. These are the current dialysis access devices of choice. Their scientific basis is described in "Fluid Mechanics of Hemodialysis Catheters," Transactions of American Society for Artificial Internal Organs, Vol. XXXI, pp. 124-130 (1985).
Certain catheters have included a third, circular lumen located coaxially in the center of the internal septum of the dialysis catheter. This construction, however, compromises the efficiency of the other two lumens, and consequently such catheters do not meet the functional requirements for hemodialysis catheters as described in "Minimum Performance Standards for Double-Lumen Subclavian Cannulas for Hemodialysis," Transactions of American Society for Artificial Internal Organs, Vol. XXXII, pp. 500-502 (1986).